The present invention relates to an improved image-transfer-type electrostatic recording apparatus in which an endless-belt-shaped latent-electrostatic-image-bearing recording medium is trained over a drive roller and a driven roller which are supported by a frame member, and is rotated, and the latent electrostatic images are developed to visible images during the rotation of the latent-electrostatic-image-bearing recording medium, and the developed visible images are then transferred to a recording sheet, and there is disposed a device for correcting the skewing of the endless-belt-shaped recording medium by moving upwards or downwards one end portion of the driven roller. More particularly the present invention relates to an electrostatic recording apparatus of the above-described type, comprising a recording sheet guide means which is substantially integral with the above-mentioned frame member and/or driven roller, thereby guaranteeing appropriate contact of the recording sheet with the recording medium.
In an image-transfer-type recording apparatus, such as electrophotographic copying apparatus, electrophotographic offset master making apparatus, electrophotographic printing apparatus or facsimile apparatus, as a latent-electrostatic- image-bearing recording medium, an endless-belt-shaped photoconductor or dielectric material is employed as well as a drum-shaped photoconductor. In the case of the endless-belt-shaped photoconductor or dielectric material, if one peripheral length is slightly different from the other, or if the diameter of one end portion of a drive roller or driven roller for rotating the endless-belt-shaped photoconductor or dielectric material is slightly different from the diameter of the other end portion of the drive roller or driven roller, the endless belt is gradually skewed as it is driven in rotation by the drive roller. As a result, the endless-belt-shaped photoconductor may be damaged in the edge portions, and normal latent electrostatic image formation or image transfer may be interfered with, particularly in the side areas of the photoconductor.
For avoidance of such shortcomings, conventionally one end portion of a driven roller is slightly moved horizon-tally or vertically relative to the drive roller to counter the skewing of the endless-belt-shaped photoconductor during the rotation thereof.
Referring to FIG. 1, there is shown a schematic partial view of a conventional electrostatic recording apparatus which permits vertical positional adjustment of a driven roller 2 relative to a drive roller 1 through a frame member which supports the drive roller 1 and the driven roller 2, in order to counter the skewing of an endless-belt-shaped photoconductor 3.
In the electrostatic image recording apparatus shown in FIG. 1, if one end portion of the driven roller 2 is moved upwards or downwards for countering the skewing of the endless-belt-shaped latent-electrostatic-image-bearing photoconductor 3, not only the distance between the photoconductor 3 and an image transfer charger 4, but also the distance between the photoconductor 3 and a recording sheet guide member 5, is changed, since the recording sheet guide member 5 is integral with the image transfer charger 4. As a result, a recording sheet 8, when transported, deviates from its predetermined transportation path. In particular, when the recording sheet guide member 5 is moved beyond a certain range away from the photoconductor 3, the recording sheet 8 cannot be brought into close contact with the photoconductor 3 in a predetermined image transfer section thereof as illustrated in FIG. 2. As a result, for instance, blurred images are formed at a side portion of the recording sheet 8, or no images are formed thereon.
Such problems could be solved if the image transfer charger 4 were designed so as to be integral with the recording sheet guide 5, and also to be movable together with the photoconductor 3 when the driven roller 2 is moved upwards or downwards in order to counter the skewing of the photoconductor 3.
However, the image transfer charger 4 is usually fixed to a guide rail member 7 through a spring plate 6 or the like as shown in FIG. 1. Therefore, it would be impractical to move the image transfer charger 4 against the resilience of the spring plate 6 or the like. It would also be impractical to move the image transfer charger 4 together with the guide rail member 7, since a very complicated mechanism would be necessary for attaining such movement of the image transfer charger 4.
Furthermore, in the above-described conventional electrostatic image recording apparatus, since the recording sheet guide 5 is disposed separately from the previously mentioned frame member for supporting the drive roller 1 and the driven roller 2, and from the driven roller 2 as shown in FIGS. 1 and 2, it is extremely difficult to dispose (i) the recording sheet guide 5 and (ii) the photoconductor unit comprising the drive roller 1, and driven roller 2 and the frame member with the endless-belt-shaped photoconductor 3 trained over the two rollers 1 and 2, with a predetermined space accurately maintained between the recording sheet guide 5 and the photoconductor unit, particularly in the manufacturing process.